1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor substrate.
2. Description of the Related Art
In recent years, integrated circuits using an SOI (silicon on insulator) substrate, instead of using a bulk silicon substrate, have been developed. By utilizing the characteristics of a thin single crystal silicon layer formed over an insulating layer, transistors formed in the integrated circuit can be completely separated from each other, and further, the fully depleted transistors can be formed. Accordingly, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
As a manufacturing method of an SOI substrate, a hydrogen-ion-implantation separation method in which hydrogen ion implantation and separation are combined is known. A typical process of the hydrogen-ion-implantation separation method will be described below.
First, hydrogen ions are implanted into a silicon substrate to form an ion implantation layer at a predetermined depth from the surface. Next, a silicon oxide film is formed by oxidation of another silicon substrate which serves as a base substrate. After that, the silicon substrate into which the hydrogen ions are implanted and the silicon oxide film on the other silicon substrate are firmly attached to each other to bond the two silicon substrates. Then, heat treatment is performed, whereby one of the silicon substrates is cleaved using the ion implantation layer as a cleavage plane.
There is a known method in which a single crystal silicon layer is formed over a glass substrate by using a hydrogen-ion-implantation separation method (e.g., Reference 1: Japanese Published Patent Application No. H11-097379). In Reference 1, a separation plane is mechanically polished in order to remove a defect layer formed by ion implantation or a step in the separation plane.